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Newcastle disease (ND), called exotic Newcastle disease (END) in the U. S., is the more important of the two clinical disease forms caused by Newcastle disease virus (NDV) infections of poultry and other bird species and is a world wide threat to poultry production. The cause of END is an infection with a virulent NDV strain as classified by the international standard molecular and chicken inoculation tests. The U. S. is considered free of END in poultry because all recent outbreaks have been eradicated. In contrast, infections with low virulence strains of NDV are endemic in U. S. poultry and cause a typically mild clinical disease form with primary involvement of the respiratory tract.

The occurrence of END in commercial poultry is reportable to the World Organization of Animal Health (OIE) and impacts international trade in poultry and poultry products. The two most devastating END outbreaks in the U. S. have occurred in Southern California. The first of those occurred during 1971-1974, was traced to the importation and release of infected exotic pet birds, and cost over $56 million in Federal funds to eradicate. The second occurred during 2002-2003, started in back yard holdings of illegally imported game fowl, and eventually spread to commercial poultry. Over $180 million in Federal funds was expended to eradicate that outbreak. Although virulent forms of END virus have been eradicated from poultry, they are periodically recovered from illegally imported pet and game birds and from migratory water-birds, particularly the double-crested cormorant. These sources of virulent NDV are a continuing threat to the U. S. poultry industry.

Strains of NDV are all members of the same serotype, avian paramyxovirus type 1 (APMV-1), but vary in virulence. Consequently, the rapid differentiation of virulent viruses, the cause of END, from the low virulence strains causing the non-reportable NDV infections is extremely important. Recent research accomplishments include utilization of nucleotide sequence analysis of the virus genome to differentiate virulent and low virulence viruses and to develop rapid diagnostic tests based on those sequence differences, developing a novel ND virosome vaccine and confirming the efficacy of currently available vaccines against recent virulent NDV isolates, and determining the pathogenesis of NDV strains of different virulence in chickens and turkeys as well as the differing pathogenesis in chickens, turkeys, and pigeons of the END virus from the most recent U. S. outbreak.

Current objectives are to extend the molecular characterization of new isolates and thereby extend the database for conducting molecular epidemiology, to complete development of a NDV reverse genetics system, and to continue pathogenesis studies of new NDV strains and mutated viruses. The ultimate goal is to achieve a better understanding of the molecular basis of NDV virulence and to utilize that knowledge along other approaches to improve methods for control of infections with NDV.